Our first sight of King Alfred in Bernard Cornwell's historical novel, The Last Kingdom, is of him crouched shamefully outside a tent, moaning in pain, vomiting, and grovelling for God's forgiveness: "It seemed Alfred had humped a servant girl and, immediately afterwards, had been overcome by physical pain and what he called spiritual torment." Hardly the introduction we might have expected to the only English sovereign ever awarded the epithet "the great", or to the monarch whose statue defiantly holds a sword erect in the centre of Winchester. But Cornwell's portrait of a sickly and sinful young Alfred is faithful to The Life of King Alfred, a history believed to have been written in or shortly after his reign, by a Welsh bishop called Asser.

The other early source for Alfred's life is the ninth-century Anglo-Saxon Chronicle . Cornwell's novel - the first part of a trilogy set in Alfred's reign - closely follows the battles, treaties and successions laid out in this history: beginning in 867, when Alfred's elder brother Æthelred was still king of Wessex and, according to the chronicle, there was "an immense slaughter of the Northumbrians" by Viking raiders at York; and ending in 877, one year before the young King Alfred infamously - though temporarily - lost control of the last English kingdom to the dreaded Danes.

For most of this first volume, however, it is not from the scriptoria of the Saxons, but from the camps and dragon-boats of the Northmen, that the struggle for England is viewed. Cornwell chooses for his narrator a Northumbrian boy who is captured and raised by pagan Danes, before granting his allegiance to Alfred's West Saxons. Sitting between cultures, he wrestles throughout with issues of identity: "Northumbrian or Dane? Which was I? What did I want to be?" Such a scenario is not unlikely - in the north-eastern areas of the country, at that time when "England" was still being forged, there was much cultural amalgamation between Dane and Saxon. And such questions cannot help but have resonance for a modern audience, living in a post-devolution Britain that is again struggling to find an identity: English? British? European? Which are we?

For Uhtred, Cornwell's young narrator, there can be little doubt that - although he finally swears his sword to the English Alfred - his heart tugs irresistibly towards the Danes. "To exchange Ragnar's freedom for Alfred's earnest piety seemed a miserable fate to me," he muses. And it is difficult for the reader not to share much the same sentiment. While Cornwell's Danes roar with delight on the battlefield, revel in the salt-spray soaking their flaxen locks, and feast with carnivorous joy, his Saxons are mostly rule-bound, pious leek-eaters. In the historical notes to the novel, Cornwell asserts that he wished to escape the "fanciful imagery" that has become attached to the horn-helmeted figure of the Viking -but some cultural stereotyping surely remains in his depiction of the two contesting peoples.

Cornwell's rather muted Saxons follow in a tradition of disregard for Anglo-Saxon history that has prevailed since the early 20th century. In the Victorian period, Alfred's life was "the favourite story in English nurseries" and the Saxons were hailed as the founders of just about every English institution. But two world wars against a Germanic nation made Saxon heroes distinctly less attractive to English writers and film-makers than Britons, Normans or Norsemen. How many Arthurian films stand beside the sole 1969 film Alfred the Great ? Alfred has waited many years for a novelist to update the Victorian image of him as an exemplar of the sort of moral, masculine boldness touted by 19th-century writers such as Thomas Carlyle; to give us instead the Alfred identified by recent historians - a politician who had the foresight to commission a Welsh bishop to write his biography.

Certainly, Cornwell's Saxon king is a leader cast in a 21st-century mould: a subtle, shrewd ruler, he secures the loyalty of his followers as strategically as any corporation and, above all, knows the value of spin. Uhtred learns that Alfred "had never been invested as the future king", but "to his dying day, insisted the Pope had conferred the succession on him, and so justified his usurpation of the throne that by rights should have gone to Aethelred's eldest son".

Myth-making is a subject that fascinates Cornwell, and which he has explored before. Here, the martyrdom of Edmund of East Anglia - tied to a tree and used for Viking target practice - and the self-mutilation of the nuns of St Abbs, who cut off their noses to avoid rape, are deconstructed. "The tale is still sold as evidence of Danish ferocity and untrustworthiness," Uhtred states of the latter story. "I remember one Easter listening to a sermon about the nuns, and it was all I could do not to interrupt and say that it had not happened as the priest described." Religious propaganda, in particular, receives short shrift in this novel, as in Cornwell's Arthurian trilogy. And its anatomy of how a Danish invasion in search of land and riches is conceptualised by English monks into a "holy war" surely has contemporary relevance.

Cornwell's foregrounding of the constructed and politicised nature of histories gives him a licence to stir around his sources. The reader forgives slight deviations from them, or minor chronological rearrangements in the novel (an 878 battle in 877) because, after all, who knows how accurate Asser's account is? Some slips, though, might remain inexcusable to the avid Anglo-Saxonist: twice in this novel, Alfred's name mysteriously mutates to "Arthur" - the king who, throughout the 20th century, has so effectively supplanted the Saxon as the nation's favourite medieval monarch.

It is difficult not to view this as portentous. Alfred may blossom from sickly lecher to triumphant hero in the remaining two volumes of this series. But if even Cornwell cannot shake off the shadow of the Excalibur-wielding Celt, then it remains to be seen whether, for near-forgotten Alfred, The Last Kingdom will represent a renewed role as national icon - or just the last gasp.

· Joanne Parker is junior research fellow in the department of historical studies at Bristol University.